The present invention relates to an occlusion device for use in occluding a septal wall. More specifically, the present invention relates to a fully retrievable occlusion device having occluding sheets made by laminating two or more sheets of polyvinyl alcohol foam together.
The heart is generally comprised of four chambers, the left and right atria and the left and right ventricle. Separating the left and right sides of the heart are two walls, or septa. The wall between the two atria is the interatrial septum, and the wall between the two ventricles is the interventricular septum. There are several cardiac defects which can both children and adults, including patent ductus arteriosus, patent foramen ovale, atrial septal defects (ASDs), and ventricular septal defects (VSDs).
Normally, permanently repairing septal or other cardiac defects in adults and children requires open heart surgery; a high risk, painful and costly procedure. In response to these concerns, modern occlusion devices have been developed to treat certain septal defects. Rather than surgery, these occlusion devices are small enough to be deployed by inserting a catheter into a major blood vessel and moving the occlusion device through the catheter. This type of procedure can be performed in a cardiac cathlab, and avoids much of the risks, cost, and pain associated with open heart surgery. Such occlusion devices can be used to treat a wide range of cardiac defects, including patent ductus arteriosus, patent foramen ovale, atrial septal defects, ventricular septal defects, and can be used to occlude other cardiac and non-cardiac apertures.
Occlusion devices that can be inserted via a catheter include button devices, collapsible umbrella-like structures, and plug-like devices. Occlusion devices with umbrella-like structures use a system of small metal wire arms to hold the occlusion device in place. To ensure proper seating and successful occlusion, the occlusion device must be stiff enough and have enough tension so that the occlusion device will remain in place even as the heart pulses. In addition, the occlusion device must have a high cycle life, so that it does not develop fatigue failure problems or break due to the constant flexing of portions of the occlusion device caused by the beating heart. Lastly, the device must have a suitable tactile response so that when it is deployed, the physician can “feel” whether or not the device has been successfully deployed at the defect.
Each of these design features compete with the other, making it difficult to design an occluder which adequately addresses all of them. Increasing stiffness may increase the tactile response, but may also lead to a decreased cycle life. This is because increasing the stiffness typically involves varying the shape and increasing the diameter of the wires used in occlusion devices. However, increasing the diameter of the wire to improve its stiffness or strength often reduces the cycle life because a larger diameter wire is often more brittle, and thus more susceptible to fatigue failure. Conversely, using smaller, thinner wires may result in increase fatigue life, but may also reduces the ability of the occlusion device to successfully occlude the defect, and may adversely affect the tactile response felt by the physician.
Another design challenge lies in designing sheets which attach to the wire arms. It is desired that the sheets be very thin, so that even when folded for insertion into a catheter, the occlusion device can fit into the smallest possible catheters. However, the sheets must likewise be thick enough that when the device is deployed, it provides the desired occluding effect. The sheets must also be strong enough to withstand the environment of the heart, and must be attached to the arms of the occlusion device in such a way that the sheets do not tear away from the occlusion device during passage through the catheter, or during and after implantation.
A further challenge in designing occlusion devices comes when designing the device so that it can be withdrawn if improperly deployed. Most occlusion devices are not retrievable. In instances where an occlusion device has been improperly deployed, correction of such improper deployment can often only be achieved by resorting to open heart surgery. Similarly, open heart surgery is required in instances where the occlusion device has embolized. Even if the device is partially retrievable, it may require inserting a larger catheter to accommodate removal of the occlusion device. Also, if retrieval is possible, the occlusion device is often not reusable. Rather, the first device must be removed and a second, new occlusion device must be loaded into the catheter for insertion. The result is a longer more complicated procedure and increased expense.
Thus, there is a need in the art for an occlusion device having occlusion sheets which are thin enough to allow the device to be passed through a catheter, yet strong enough to provide the desired occluding effect and remain attached to the occlusion device during deployment and insertion. There is also a need in the art for an occlusion device that can be fully retrieved through the same catheter used for deployment.